Specialeforsvar: Anne Bækbo Hinke

Bikarbonat-udnyttelse hos ferskvandsplanter

Vejledere: Kaj Sand-Jensen og Ole Pedersen

Censor: Brian K Sorrell, Århus Universitet

Abstract
The ability of macrophytes to utilize bicarbonate as source of inorganic carbon is affected by the environmental availability of dissolved free CO2 and bicarbonate. Freshwater lakes and rivers in the tropics generally contains lower amounts of bicarbonate than temperate freshwaters, and therefore a lower proportion of tropical species may be able to utilize bicarbonate compared to temperate macrophyte species. The aim of this study was thus to investigate if the frequency of bicarbonate users differed amongst tropical and temperate freshwater plants. Data were either collected through laboratory experiments with 16 tropical and 3 temperate species of freshwater plants, or from a comprehensive literature review. The ability to utilize bicarbonate was investigated by pH-drift experiments, and by measuring underwater photosynthesis at moderate bicarbonate concentration (2.0 mmol L-1) but at different CO2 availability (1 or 500 mol L-1). Prior to the experiments the plants were grown for an acclimation period in the laboratory at moderate alkalinity and high light intensity, but at low CO2 availability for at least 14 days to stimulate synthesis of proteins essential for bicarbonate use. As a result, 2 of the 16 tropical species and all 3 temperate species were able to utilize bicarbonate. The experiments showed that bicarbonate users could maintain high photosynthetic rate at low CO2 availability. Ceratophyllum demersum collected in the tropics and in temperate areas, respectively, showed that the same species can either possess or lack the ability to utilize bicarbonate. The metaanalysis included 97 species of which 24 were tropical and the proportion of bicarbonate users was 33% for the tropical species and 52% of the temperate species, but this proportion was not statistically significant among tropical and temperate species. The conclusion is based on a limited number of tropical species and a sensitivity analysis showed that only 4 species of tropical CO2 users are required to change the statistical outcome.